How close we are to replacing guide dogs with AI?
Chieko Asakawa (wiki, TED, IBM) is a major researcher in this area, and the linked TED talk is probably a good introduction to the state of the art as of 2015. Here's a link to a 2016 paper on a smartphone navigation system.

Guide animals perform manipulation tasks as well as identification tasks, and so it's not clear if those could be replaced well at all. (A smartphone that reads a label is a great help, but a dog that knows which bottle to grab and deliver to you is probably a much better help.)